Since your PC is from Dell, than check and double confirm that the IDE cable on your CD/DVD Rom is an 80wired cable that supports ultra133.Most Package Pcs form Dell, HP, Compaq....etc only bother to install only on the Hardisk side that is the Primary channel and use a normal 40 wired cable for the Secondary to save cost.If you dont know how to count or recognise an Ultra133 cable than by all means go out and buy 1 that is labeled.Another solution is to check your Motherboard Chipset weather its supporting UltraDMA133. If its support than go to Dell webside and download the latest bios. If Dell does not available, normally What I did was to check the Original manufacturer and Model of the MotherBoard and go the the Original manufacturer and download the latest Bios from them. Usually for my case it will work, only thing is that the original Dell or whatever bios will be wipe out.Flash the bios at your own risk.

Last four digits are likely 0001, 0002. Under those keys you will find MasterIdDataChecksum, SlaveIdDataChecksum. Delete the value corresponding to your drive. It will make the OS to redetect the device DMA capabilities after reboot."

Put your Nec Slave and CD-drive Master . I solved my dma problems this way. I have cd-writer Plextor in multi-word dma mode and if it was Slave and my Nec was Master, Nec accepts only PIO mode. Hope this will solve your problems.